Methods for control of the texture level of yarn produced by moving cavity texturing apparatuses are based on the principle of constant volume displacement per unit time. For a predetermined yarn speed, as measuring at the inlet to the moving cavity texturing apparatus, changes in the position of the end of a plug formed in the moving cavity are monitored and used to generate a feedback signal. The feedback signal can then either cause a change in a fluid pressure or temperature or a change in the speed of the moving cavity. Increasing or decreasing the fluid pressure or temperature causes a corresponding increase or decrease in the packing density of the plug and thus increases or decreases the mass flow per unit time for a given volume displacement. Increasing or decreasing the packing density of the plug produces a correspondingly higher or lower texture level.
The plug contains many yards of yarn, which results in a considerable time lag between the time when the yarn passes the location where texturing is occurring, and the time when the yarn reaches the end of the plug where monitoring takes place. The result is that the yarn, although it may have a uniform overall average texture, has local variations between short, adjacent yarn segments. These local variations will show up as machine barre in knitted fabrics.
The texture level of the yarn produced by the moving cavity texturing process disclosed in U.S. Pat. No. 4,074,405 is controlled by monitoring the position of the end of the plug. This procedure suffers from the time lag between the time of monitoring and the time of texturing, as discussed above.